As this kind of peer to peer type information delivery system, there is known a method of enhancing fault tolerance and property of distributing accesses by distributing and allocating (distributing and storing) delivery information (e.g. content data) in plural node devices participating in the system. Location of the content data thus distributed and stored can be efficiently searched for by use of a distributed hash table (hereinafter referred to as “DHT”) as disclosed by for example non-patent document 1. This DHT is memorized in respective node devices, and transfer destination node information (including e.g. node ID, IP address and port number unique to the node device) indicative of plural node devices to which the message is addressed is registered in the DHT.
For example, in a case where the above-mentioned content data are stored in a given node device, the node device sends out a registration message (including content ID unique to the content data and storage source node information indicative of the node device), which indicates a registration request of storage source node information (including e.g. IP address and port number) indicative of the node device, to the other node devices. The registration message is transferred to the source node device managing a content data location (to the root node described later) by plural relay node devices according to the above-mentioned content ID and DHT, the storage source node information is memorized in the management source node device and managed. Further, the storage source node information is also memorized and managed in the above-mentioned plural relay node devices in the transfer route of the registration message.
Then, the node device desiring to acquire the above-mentioned content data sends out content location inquiry (search) message (including the content ID and the node information indicative of the node device) searching the location of the content data to the other node device. Then the content location inquiry (search) message is transferred to the node device managing the content data location by plural relay nodes devices (in some cases the relay node devices corresponding to the relay node devices in the transfer route of the registration message, and in other cases they being not). In a case where the relay node device located in the transfer route manages the storage source node information, the node device sending out the content location inquiry (search) message acquirers the storage source node information from the relay node device. In a case where any relay node devices existing in the transfer route do not manage the above storage source node information, the storage source node information is acquired from the management source node device which the message finally reaches. Accordingly, the node device sending out the content location inquiry (search) message is enabled to acquire the content data from the node device specified by the storage source node information.
Non-Patent Document 1: “Lightweight Load Balancing for Distributed Hash Tables”, Institute of Electronics, Information and Communication Engineers